Deadlift attempt at 170kg or 375lbs

I have been successfully lifting upto 160kgs for the last 2 months, but have not managed to go beyond that.
I can think of several reasons for it:
1. Diet is not proper
2.Flexibility needs more work
3. Need to start creatine for a month to get to the next level.
4. Should try and do some rack work before I can do floor lifts

This is my attempt at 170kg or 375 lbs.Technique is all over the place. While coming up, I could keep my back straight to some extent, but the bar started slipping around midway. I could not manage to hold the weight for long in an upright position and while coming down the back was all over the place!
Another problem is, when I am doing the deadlift with an inverted grip, I can only pull with the right hand overhead and the left hand inverted. To get uniform development on both sides I should be able to alternate between the grips.I can comfortably do it upto 130kgs, but over that it is a bit hard.
I need to do some good deadlift work with an overhand grip for around 120kgs. After I have comfortably done around 12 to 14 reps of it, maybe then I can proceed with the 1-RM at 170 and beyond.
200 before year end awaits! :)